Acute allergic reaction including anaphylaxis, is a systemic, immediate hypersensitivity reaction caused by exposure to a specific antigen. The immune system activates immunoglobulin E (IgE), which reacts with effector cells (mast cells and basophils). These cells, in turn, release histamine, serotonin, leukotrienes, and prostaglandins, and induce a range of signs and symptoms, such as facial flushing, urticaria (hives), edema, pruritus, broncho-constriction, cough, cardiac arrhythmias, hypotension, nausea, vomiting, and diarrhea. Cutaneous manifestations are most common, with urticaria and angioedema present in 88% or more of patients experiencing acute allergic reactions. Swelling in the airway is the most life-threatening symptom, commonly causing dyspnea, wheezing, stridor, and upper airway obstruction from severe edema. Cardiovascular symptoms include dizziness, hypotension, and syncope related to third-spacing of intravascular fluid. Common gastrointestinal manifestations include nausea, vomiting, abdominal pains or cramps, and diarrhea. Although symptoms vary between acute allergy patients, onset generally occurs seconds to minutes after exposure to an antigen and requires prompt treatment.
The true incidence of acute allergic reactions including anaphylaxis is unknown, partly because of the lack of a precise definition of the syndrome. Some clinicians reserve the term anaphylaxis for the full-blown syndrome, while others use it to describe milder cases. Fatal anaphylaxis is relatively rare; milder forms occur much more frequently. The frequency of acute allergic reaction is increasing, and this has been attributed to the increased number of potential allergens to which people are exposed, such as increased varieties of food and medications. A recent review concluded that the lifetime prevalence of acute allergic reactions including anaphylaxis is ˜5% of the population with higher prevalence in developed countries than developing countries.
Approximately 1 in 5000 exposures to a parenteral dose of a penicillin or cephalosporin antibiotic causes anaphylaxis. More than 100 deaths per year are reported in the United States due to antibiotic induced allergies. Fewer than 100 fatal reactions to Hymenoptera stings are reported each year in the United States but this is considered to be an underestimate. One to 2% of people receiving IV radiocontrast experience some sort of reaction. The majority of these reactions are minor, and fatalities are rare. Low molecular weight contrast causes fewer and less severe reactions. Narcotics also induce acute allergic reactions.
Acute allergic reactions occur in all age groups. Food allergies are more common in the young, whereas more drug reactions occur in adults, possibly due to greater exposure to medications, including narcotics, aspirin/NSAIDs, antibiotics, IV contrast media, anesthesia, muscle relaxants, etc. Although prior exposure is essential for the development of true anaphylaxis, reactions occur even when no documented prior exposure exists. Thus, patients may react to a first exposure to an antibiotic or insect sting. Elderly persons have the greatest risk of mortality from acute allergic reactions due to the presence of preexisting disease.
Emergency treatment includes airway protection, alpha-agonists, antihistamines, steroids, and beta agonists. Medications currently used in the treatment of acute allergic reactions include epinephrine, diphenhydramine injection, corticosteroids, albuterol, and glucagon. Epinephrine is the first-line drug to be given to a patient having an acute allergic reaction. An alpha-receptor agonist, epinephrine reverses hypotension. It also has beta-receptor activity, which dilates the airways, increases the force of myocardial contraction, and suppresses histamine and leukotriene release, reducing inflammatory responses. Diphenhydramine injection is the second—line drug to be given to a patient having an acute allergic reaction as an adjunct therapy to epinephrine for the relief of peripheral symptoms such as pruritus, engioedema, hives, erythema, etc.
What is needed are additional treatments for severe allergic reactions including anaphylaxis.